Control of avian influenza in Italy: from stamping out to emergency and prophylactic vaccination.

Abstract

Since 1997, north-eastern Italy has been repeatedly challenged by avian influenza (AI) infections caused by viruses of the H5 and H7 subtypes. The penetration of such infections in the industrial circuit in densely populated poultry areas (DPPAs) resulted in massive spread, and early attempts to control AI only by stamping-out and restriction policies resulted in death or culling of millions of birds. The re-emergence or the introduction of AI viruses in the same DPPA resulted in the development of an emergency vaccination programme based on the use of heterologous vaccination and a companion discriminatory test. By enabling the detection of field exposure in vaccinated animals, the application of this system, in conjunction with a monitoring programme and a well-defined territorial strategy has resulted in the eradication of H7N1 and H7N3 epidemics that occurred between 2000 and 2004. Retrospective analysis of the AI outbreaks in north-eastern Italy coupled with surveillance programmes in wild birds and in hobby flocks indicating that certain areas are at continuous high risk of infection, was the rationale for developing and implementing a bivalent H5/H7 pilot vaccination programme in a restricted area of the DPPA. Laboratory and field evidence indicate that vaccinated animals are more resistant to challenge and shed lower amounts of virus, thus acting as a tool for both prevention and control, thus limiting the impact of AI infections.